The present invention relates generally to a chassis for an amphibious vehicle, and more particularly, to an amphibious vehicle chassis which connects adjacent pontoons so as to more effectively distribute the forces between the chassis and the pontoons thereby alleviating the sheer stress on the fasteners used to attach the pontoons to the chassis and providing added strength to the chassis connections.
Amphibious vehicles were first developed over 50 years ago primarily to support oil and gas exploration operations conducted in marshy or swampy terrain. Such vehicles typically include a pair of pontoons connected to a center platform. The pontoons are usually surrounded by a cleated track system which is capable of engaging ground, water, or swamp land to propel the vehicle. One or more endless chains are preferably driven by a sprocket, or other means, and surround each pontoon. The endless chains support the cleated tracks and are guided along the outer surface of the pontoon by guide channels. The cleated tracks are driven about the periphery of the pontoons in order to provide a thrust to the vehicle. By varying the amount and direction of thrust, or track travel, applied to each pontoon, the vehicle can be advanced, turned, or reversed.
Referring to FIG. 1, there is shown a tracked amphibious marsh vehicle 10. Marsh vehicle 10 includes a pair of pontoons 16, 18 forming a platform 15 to support a machinery 12 thereon. Machinery 12 can be selected from a wide assortment of heavy equipment but is shown in FIG. 1 as a boom crane. Pontoons 16, 18 are preferably constructed from steel or aluminum as rigid hollow structures or enclosures to provide sufficient buoyancy or "flotation" in amphibious environments to stabilize and support machinery 12 even on marshy or swampy terrain. Vehicle 10 also includes a lower drive train 14 with a driven endless track 20, 22 mounted around each of the pontoons 16, 18, respectively. A drive system (not shown) is used to independently rotate endless tracks 20, 22 about their respective pontoons 16, 18. The rotation of endless tracks 20, 22 is the primary method of positioning and guiding marsh vehicle 10. By varying the speed and direction of each track 20, 22, vehicle 10 is able to advance, change course, or reverse.
Over the years, improvements in the structure and integrity of pontoons allow these vehicles to work in more difficult terrain and operating environments. The pontoons are typically constructed of steel or aluminum alloys, are capable of flotation, and are useful for most situations where an amphibious vehicle is required. The pontoons are primarily for the purpose of supporting the deck or platform upon which the heavy machinery is mounted.
The platform and pontoons are connected and held together by a chassis. A typical chassis, along with the platform, is used to support or mount the heavy equipment, including but not limited to, excavators and personnel platforms. A vulnerable aspect of typical amphibious marsh vehicles is the durability of their chassis. The chassis is located between the pontoons and links the pontoons to the platform.
Referring now to FIG. 2, there is shown a typical prior art chassis 30. Prior art chassis 30 includes a central member 32 connecting two pontoons 34, 36 on either side thereof through two sets of flange plates 38, 40 and 42, 44 with a plurality of threaded fasteners 46. Central member 32 is constructed as a structural beam 48 with a support plate 50 welded thereupon and flanges 38, 42 at opposite ends. Pontoons 34, 36 each are constructed as hollowed steel or aluminum enclosures 52, 54 and are welded to extension members 56, 58. Extension members 56, 58 are thus welded to flanges 40, 44 which are in turn flanged up with flanges 38, 42 and bolted together by fasteners 46.
When an equipment module is placed on chassis 30, a normal force of large magnitude is applied to chassis 30 in direction W, generally perpendicular to the ground. Pontoons 34, 36 provide opposite loads and opposite bending moments P1 and P2, respectively, on the chassis 30. Ideally, when fasteners 46 are secured, force W and bending moments P1, P2 place the top fasteners, as for example fastener 46A, in compression and place the bottom fasteners, as for example fastener 46B, in tension. Under such tensile and compressive conditions, fasteners 46 must be robust.
However, when fasteners 46 are not properly secured or become loosened, shear stresses act generally along shear planes E and F causing adjacent flanges 38, 40 and 42, 44 to move in shear. Threaded fasteners, preferably in the form of bolts with corresponding nuts, are generally much stronger in tension and compression than they are in shear. Loosened fasteners 46 in prior art chassis designs can experience severe shear loads and are highly likely to fail in service. Such loosening of fasteners 46 can be the result of vibration or fatigue loading conditions. These loading conditions are highly prevalent in marsh vehicle environments and must be accommodated to prevent failure in service.
Because of the weight of the heavy equipment and the buoyant forces of the pontoons, the chassis undergoes tremendous forces. The vibratory forces and fatigue forces from the operation of the vehicle itself, the movement in the rugged terrain, the forces caused by the operation of the heavy equipment, such as an excavator, and the movement of the pontoons due to their buoyancy, prevent the long term durability of these vehicles.
Recently, demand in the industry is growing for vehicles that can perform even more rugged tasks with even heavier equipment, making larger marsh vehicles with higher load carrying capabilities necessary. Additionally, the terrain, wherein these amphibious vehicles are deployed, continues to get more and more treacherous as locations become more remote. Combined, the increase in size and the difficult terrain, mandates that the structural integrity of the vehicles meets rigorous, exacting standards. The remote locations where such vehicles are deployed also prohibits much routine and preventative maintenance. Therefore, there is a need for vehicles that can carry out operations in more remote locales and which require less maintenance.
The typical chassis is not designed to withstand these rigors and, consequently, tends to fail under such conditions. Particularly, it often occurs that the bolts that hold the vehicle chassis together, become loosened through the vibratory and fatigue loads that the chassis experiences. When chassis bolts become loose, failures in the chassis occur, pontoons become disconnected, requiring expensive and time consuming field repair operations. There is a need among the amphibious vehicle industry for a chassis that reduces or eliminates such failures. With a more robust chassis, larger amphibious vehicles with heavier equipment can be deployed in marshy regions, thus reducing the amount of time and resources required to perform many operations, such as construction or demolition, in rugged terrain and difficult environments.
The present invention overcomes the deficiencies of the prior art.